Reactor to perform chemical reactions with a disintegrating disc

ABSTRACT

The present invention provides a reactor adapted to simultaneously accomplish chemical reactions and operations of size reduction of the solid materials in suspension and particularly for treatment in the cellulose and/or paper pulp industry. The reactor provides an essentially closed working environment and is provided in the lower part with a rotor which creates turbulence with flows over essentially the whole volume of the closed environment and is adapted to realize said conditions of the size reduction of solid materials with intimate mixing of same with the suspending liquid.

BACKGROUND OF THE INVENTION

The present invention concerns a reactor which permits simultaneouschemical reactions and operations of size reduction of the solidmaterials in suspension.

Particularly, the invention relates to a reactor suited for thementioned operations and named "TURBOPULPER", adapted particularly fortreatment in the cellulose and/or paper pulp industries. This reactorhas an axial admission rotor with a radial delivery such as to create aturbulence inside the reactor. This reactor is preferably adapted tooperate under pressure and has a spherical shape and may be heated (FIG.1 and 2).

The present invention relates to a reactor for effecting chemicalreactions simultaneously with operations of size reduction of solidmaterials in suspension,. Such a reactor is particularly usable but notexclusively, for example in the alkali-oxygen process fordelignification.

As known, generally the chemical reactions are activated by a goodmixing and by adequated temperatures. The reaction is still more activewhen conditions are created for a good "exchange of materials". Amongstthese last conditions, there is the maximum possible exchange surfaceand interchange of the substances which must react along this surface.The general conditions summarized above are particularly difficult toattain in cases when the solid materials in suspension for the reactionare at high consistency in water or other liquid vehicles.

SUMMARY OF THE INVENTION

Particularly, these conditions must be reached in two separate apparatusoperating in the pulp industry and called pulper and digester. Theequipment referred to this invention provides for both these operationspreviously carried out in this industry by the aforesaid separateapparatuses. These apparatuses generally are not capable in theconditions to completely satisfy all the requirements of the particularapplications and to have at the same time the necessary flexibility toreach the optimum or nearest to optimum working conditions with thetreated materials of different characteristics.

Therefore, among the objects of the present invention is to provide anew reactor for the aforesaid uses, permitting under the mentionedconditions activation and speeding up of the chemical reactions,assuring that their effect is distributed extremely homogeneouslythroughout the reaction mass.

Particularly, one object of the present invention is to provide areactor, as mentioned above, which simultaneously presents the followingadvantages:

(a) capability to reduce the size of the particles of the solid mattersin suspension to the desired level;

(b) homogeneous distribution of chemicals throughout the mass,simultaneously with the size reduction of the solid materials insuspension;

(c) complete recycling of the contents of the reactor inside itsspherical interior so that the material passes at every cycle at leastone inlet zone of the chemicals fed in continuously; and

(d) possibility of indirect heating, i.e., the heating medium is notmixed with the suspension to be heated, and without the well knowninconveniences deriving from the formation of deposits of the suspendedmaterials on the hot surface and thus maintaining a high constantcoefficient of heat exchange independently from the type of suspension.

According to the invention, these and other objects are realized due tothe fact that the reactor provides an essentially closed environment oftreatment, where, in the lower zone, a rotor preferably with axialadmission and radial delivery creates a turbulence with flows normallyover the whole volume of the closed environment and at the same time,performs also the said size reduction of the solid materials mixing themintimately with the suspending liquor. The closed environment, asdefined by the reactor, may advantageously be put under asuper-atmospheric pressure. The reactor is of an essentially sphericalshape and is heated indirectly, for example by means of steam.

The presence of the mentioned rotor, operating as aforesaid creates aturbulent motion depending on the choice of the structure and workingcharacteristics of the rotor, to obtain the desired size reduction ofthe solid particles in suspension, optimizing the reaction conditions.The turbulence furthermore cooperates to distribute homogeneously thechemicals, which are fed near the rotor, throughout the mass.

For some treatments, the best operative conditions are realized when thereactor is put under super-atmospheric pressure and is of an essentiallyspherical shape. This configuration is of particular importance inasmuchas simultaneously the following objectives are achieved:

(a) to obtain the minimum possible ratio between the reactor's surfaceand its useful volume, reducing the overall dimensions;

(b) to reduce to the utmost the thickness of the walls of the reactorespecially in the case when operating under pressure and consequentreduction of the weight and cost of the equipment;

(c) to realize, downstreams of the turbulent motion phase created nearthe rotor, guided uniform flows on the whole arc of 360° and on thedifferent levels where the flows are developing; and

(d) to get indirect heating of the reactor for ex. by means of steam,without any danger of scaling by solid matters on the heated surfacesand hence maintaining a good heat exchange coefficient, thanks to theturbulence and to the flows formed.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be further described by way of theaccompanying drawing in which:

FIG. 1 is a lateral view of a reactor according to one embodiment of theinvention.

FIG. 2 is a partial sectional view following to a plane passing throughthe vertical shaft of the reactor and illustrating the parts of therotor.

FIG. 3 is a sectional view substantially along the line III--III of FIG.2.

FIG. 4 is a plan view of an alternative shape of the impeller of therotor.

FIG. 5 represents schematically the currents inside the reactor.

FIGS. 6, 7 and 8 are schematic illustrations of the use of the reactoraccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing and initially to FIG. 1, the reactor isessentially formed by a spherical body 10 which may have for example adiameter up to 10 m. (500 cu.m of useful volume) supported by verticalrods 11.

A shaft 12 is disposed in the lower part of the container 10 and extendsoutside through an adequate stuffing box controlling the rotation of therotor.

This shaft 12 may be driven through a control group 13 by means of abelt transmission, gear reducer or gearmotor. A gear motor is preferredwhen a strong mechanical action is required for the size reduction ofthe suspended material requiring high power absorption with a powerdemand up to 1000 kw.

The material to be treated is charged into the container or reactor 10through the charging opening 14 preferably arranged on the upper part,whilst the discharge is made through the outlet 15 connected to thebottom of the container. This procedure of feeding and discharging thematerial is used when the equipment operates in batch or is the firstone of a series for continuous operating.

However, in case of continuous operating or for special applications,the flow may be inverted by feeding through the connection 15 anddischarging through the connection 14.

As indicated, the reactor is preferentially heated indirectly by meansof a heating fluid, generally steam, which enters in 16 and exitspreferably as condensate at 17, after having been put in contact withheat exchanging surfaces or elements, as can be seen better in thefollowing. Liquid or gaseous chemicals are admitted through thecorresponding connection 18, whilst the gases produced by the reactionare discharged at 19, preferably under the control of a pressureregulator and analysis of samples of the discharged gases. Eventualsafety and control devices, normally required for pressurized vessels,as for ex. manometers and safety valves, may be installed at the offtake20.

The internal portion of the reactor container 10 in the zone of theturbulence formation is illustrated in detail in FIGS. 2, 3 and 4. Theyshow how the shaft 12 entering the reactor through the stuffing box 21,carries the rotor 22 and the rotating disc or ring 23 fixed theretowhich cooperates with the lower stationary disc 24 with a perforatedzone 25 through which the material to be treated or the treated materialleave or enter by way of the connection 15. The disc 24 and thedefibrating discs fixed thereto are crossed by the duct 26 connected tothe inlet 18 permitting admission of liquid and/or gaseous reagents intothe mixing and laminating zone 27 between the discs 24 and 23. The gapof this zone 27 or interspace between the static disc 24 and therotating disc 23 can be varied with the machine working to better adjustit to the desired mechanical treatment to be performed. For the samereasons and depending on the material treated, the surfaces of the discs23 and 24 may assume different structure characteristics as for example,blades, stakes, abrasive surfaces or the like.

The rotor 22 and the defibrating disc 23 are structured as an impellerof a helico-centrifugal pump with axial admission and radial delivery.Indeed in the central part, the spokes 28 which bring the disc intorotation are profiled as a section of a screw for suspensions at higherconsistencies and low speed of rotation (10-200 R.P.M.) or a properpropeller in case of suspensions at lower consistencies and higher speedof rotation (200-1500 r.p.m.).

The centrifugal part of the pump is formed by the surfaces of therotating disc 23 and the corresponding channels between theaforementioned blades, stakes or abrasive surfaces.

The rotor 22 with disc 23 may be substituted by an open agitator of thetype shown at 29 in FIG. 4, especially when the treatment does notrequire an energy consuming action of defibration or disintegration.

The action of the impeller or helico-centrifugal pump causes, incooperation with proper baffles 30, circulation of the treated mass ofthe type shown in FIG. 5, where it may clearly be seen that thesuspension, guided by the baffles 30, radially leaves the pump and movestowards the top following the shape of the spherical wall and thenconcentrates at the top from where it falls down forming a centralcolumn 31.

It has thus been shown that the apparatus is of particular efficiency toachieve the desired object mentioned herein. Furthermore it was possibleto heat indirectly the suspension during the treatment by letting theheating fluid through connections 32 (FIG. 1 and 3) into the spacedefined by the baffles 30 between their surface and the wall of thereactor's shell; space which consequently is not in contact with thesuspension during the treatment. The steam circulating inside thebaffles 30 is discharged through connections 33 (FIG. 1) and heats tothe desired temperature the external surface 34 (FIG. 3) of saidbaffles, the number and shape of which may vary depending upon thequantity of heat to be transmitted to the suspension. On the outside,the baffles are contacted at high speed by the suspension pushed by thehelico-centrifugal rotor, creating the conditions for a good heatexchange which is maintained during the operation because scaling anddeposits on the surface 34 are avoided. The heating fluid or steamcondensate are recovered through a distribution ring 35 (FIG. 1) andthen passed through a heat source and again sent back in a closed cycleto the upper distribution ring 36.

The reactor herein described and called "TURBOPULPER" can be used forbatch operations as shown schematically in FIG. 6 or in continuousoperations by putting in series two or more reactors of the same type(FIG. 7). The turbopulper could also be used for continuous operations,where a homogeneous distribution of reagents and O₂ is achieved, sizereduction of the suspended material and heating to the reactiontemperature is obtained, whilst the necessary retention time for thecomplete development of the reaction is obtained in another staticcontainer 37 of an essentially conventional type, also this pressurizedand of suitable shape, in series with the turbopulper.

When the apparatus is used, as in the preferred case, to achieve optimumconditions for a delignification treatment (cook) following thealkali-oxygen process, it overcomes the mentioned difficulties of theknown treatments, represented particularly by the indirect heating of acellulose-fibres (from wood or short cycle vegetables, straw, etc)suspension in a liquid, achieving a progressive size reduction of chipsor fibre bundles from wood or annual plants with an increase of thetotal contact surface.

The apparatus performs also a perfect distribution and intimate mixingof the reagents with the fibres in suspension. Moreover, in the case ofthe mentioned treatment, yields and activates the quantity of the oxygenrequired for the delignification of the fibrous material, overcoming theproblem of the low solubility of oxygen in water and particularly at thetemperatures required to obtain the delignification (100°-180° C.).

The capacity of the apparatus to distribute gas in liquid, creates asolution within the permitted limits of the equilibrium conditions andat the same time produces an emulsion of gas in the liquid medium, thusgiving rise to a continuous contact and replacement of O₂ on the surfaceof the single fibres or bundles, which must be delignified.

As indicated herein, the reaction is eased by a simultantous mechanicaldefibration of the fibres. The reactions are speeded up by thesimultaneous indirect heating.

The turbopulper operates at consistencies of the fibre suspensionbetween 3% and 15% depending on the type of material in suspension andon the quantity of liquid necessary to contain the required quantity ofO₂ as a solution-emulsion for the delignification.

The quantity of active O₂ in a liquid solution-emulsion, may reach 10%of the dry cellulosic fibres contained in the reactor. The volume of theapparatus or of each one in the case of operating in series, is chosenso as to achieve reaction times which may vary between 30 minutes and 3hours.

The heating medium (generally steam) has characteristics which permitthe heating up to temperatures which may vary between 60° C. and 180° C.The turbopulper is tested for working pressures up to 20 bar.

The pressure naturally depends from the performance required by theapparatus and is the equivalent of the partial gas (O₂) pressure plusthat of the vapour at the corresponding working temperatures.

I claim:
 1. Apparatus for reacting a solution of cellulosic pulpmaterial under intimate and turbulent contact with a chemicalcomposition while simultaneously subjecting the pulp material to adisintegrating treatment, said apparatus comprising:(a) a stationarypressure-sealed substantially spherical reactor vessel in which the pulpmaterial is received and treated under conditions of elevated pressureand temperature, said reactor vessel having a top portion and a bottomportion for admitting the material to be treated and for discharging thetreated material, respectively; (b) a rotor member mounted to rotatewithin said reactor vessel adjacent said bottom portion, about asubstantially vertical axis; (c) a stator disc in said bottom portionspaced from and facing said rotor member to define a disintegrating areatherebetween; (d) a helico-centrifugal pump connected with said rotormember for conducting said pulp material axially into saiddisintegrating area by the aspirational effect generated by the rotationof said rotor and simultaneously generating an impeller action effectiveto eject the pulp material radially outwards from said disintegratingarea and thence in a generally upward direction in turbulent flow withinthe confines of the walls of said spherical reactor vessel withconsequent enhancement of the disintegrating action; (e) means forinjecting said chemical composition into said disintegrating area; and(f) baffle elements extending along the walls of said reactor vessel forindirectly heating said pulp material while it is being treated in saidreactor vessel.
 2. Apparatus according to claim 1, in which said baffleshave a substantially V-shaped section with vertex facing inwardly intosaid reactor vessel.
 3. Apparatus according to claims 1, or 2, in whichsaid rotor member and said stator member are provided with cooperatingshearing elements for enhancing the disintegrating action.
 4. Apparatusaccording to claim 1, in which said rotor member and said stator memberare relatively adjustable to vary the width of said disintegrating zone.5. Apparatus according to claim 1, in which said reactor vessel isconstructed to withstand an internal absolute pressure of 20 bars and atemperature of 180° C.